Radio direction finding



June 29 1926. ,5

. L. M. CLEMENT RADIO DIRECTION FINDING Filed Sept. 25, 1920 Patented June 29, 1926.

barre stares a means rarest orrics.

LEWIS M. CLEMENT, OF EAST ORANGE, NEVI JERSEY, ASSIGNOR TO ESTER/N ELEC- TRIO COMPANY, INCOR?OBATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

' Application filed September 25, 1920.

to the receiving station the bearing of the.

reference station by means of signal impulses.

A particular object is to make possible theaccomplishment of the above mentioned object by means which involves the use of an undamped wave source of propagation.

Other objects of the invention will appear more fully hereinafter. I

The invention comprises. in substance, the transmission of a modulated undamped wave in direction finding to simulate, in effect, the highly damped wave radiated from a spark source such as has-been used in. direction finding systems heretofore.

The system of this invention is applicable generally as a means for enabling a radio receiving station to obtain its bearings by means of observations based on the direc:

tion of received radio impulses transmitted from a reference station, the position of which is known. The invention is particularly applicable as an aid to navigation, both in air and on water, to enable a navigator todetermine, for example, his geographical position. This he can accomplish by taking bearings on two reference stations,

and calculating his position by triangula- 5 tion, a method entirely analogous to that used in surveying.

It may be suflicient, in particular cases, to determine his bearings alone, with reference to a known transmitting station. For in- 4 stance, the reference station could well be used to mark the location of the home sta- ,tion.of a scout-plane flying over strange and hostile territory. In this case, the knowledge of the position of the plane would be only slightly more valuable than a knowledge of its direction. The situation would i be somewhat different in the case of a ship, which would ordinarily require to know its position as well as its bearing in order to 59 enable it to'set the proper course for a port of call not necessarily on a line between the ship and the reference station, or to enable it to steer a devious course to avoid perils of navigation. It is obvious that a detertion-ptthe beari th r er ne to RADIO DIRECTZGN FINDING.

Serial No. 412,807.

'a known point may at least enable the navigator to check the accuracy of his instru- .ments, even thouglr it does not inform him of his position.

Although the discussion of the possible use broadly of the system of direction finding has been illustrated by particular reference as to its use as a navigation aid, its use is by no means confined within such narrow limits. That it is so generally considered is, possibly, due to the impulse recently given to'development in radio goniometry on account of war conditions, in which systems of the generic type above described were principally used for that purpose. It is capable of use at land stations to determine accurately the direction of the transmitting station. Many other uses will readily occur to one versed in the art, and further illustration will not be given.

A svstem embodying broadly the features of this invention requires a reference station continually sending out signal impulses and a receiving station to receive the impulses. The receiving station must include means for determining accurately the direction from which the received signals emanate. Means adaptable for use in this invention may be any one of the types, of which there are several, of directive receiving circuits. Receiving means of this general type have been developed for other uses and have beenbrought to a high state of perfection for prevention of interference. They are very commonly of the Bellini-Tosi type although they may consist of a single loop. The Bellini-Tosi type is characterized by the conjoint action of a fixed and a movable receiving conductor, one of this type being shown in Fig. 2. A report of tests on direction receiving coils especially adaptable for use onairplanes is contained in the United States Bureau of Standards Scientific Paper No. 353.

Having given a station continually send ing out signals and a receiving circuit capable of determining the direction of incidence of received signals, there is required only a means to insure that the direction from which the incident waves proceed indicates accurately the direction of the sending station, and the meansof the invention is designed to accomplish this purpose.

The phenomena of reflection and refraction of radio waves have been known for a V eonsidel ablejrti ne and have 'hee1i-.ohstiele's to thedevehpment' ofidireetion findingsys telns. The ejtfeet of these,phenomena is that the; direction otthe resultingincident iwja' vej inz y 'yaty' eonside a-bly from the direotion of the sending station; 7 The incident wave would consist of the superposition(iffthe' l phenomena efedited fbi o'a'diy vtofj 'e- I [fiCt'lfO11 and refraet'ion effects (have been as embed ar o sly to reflection and reflection Lefteets duentd the eondue'tiver"poekets in i the Te'zirth Which, "tendi to" produce he 7' change" of we ve fifont ininen-ner somewhat analogous to the retra e'ti'on3offlightat ensxnitting me 21 When it Wa ve ti eveis i11 z i""ciireetioi1 iosely' parallel torn shore of salt" Water, defied i 1 which pio' noes". thisefi e etand"the sndjcen geha nge at that tnne ln the lntenslty off-the; 4o"

'tio

incident" on" the? receiver, 3 and aeeoidin iy wo'nld not contributetheir effect 't'ofVaiy x1e i-ent direction of etheftfensinittingjstii b v' causing-Etheresultant CiLlTQCtIOII- Q I ,inelc ent Waves-to bedifiment from the dire-e- 1 ti'on ofthe directly tmnsm tted signaii Itiisi i an; object of all systemsfo direction-finding to, oid the 'reeeptlon of all w'e ves, exceptthose whleh oceed dneetly from thetzfa'nsto masses of ioniied" a1 v to'the presenee ,clouds, and: to diff-ere the .boundiariesqof the f nldf the erratic results obtained -dfQYY11 suggests'e; eomnion ea rec eivedsignal Mich hesb'een the st 'Elxpe iinents by" A". H. 7 Ta Y ihty of he e-f cnr ee eeeiv ng a :19 q'nesfiforerection fine- Vnt 'e'ha-nge the d'iree tion th He conclu en- 1" t me enome-eve? ground that definite and persistent interfere ressiv'e change in thewaveff d'einpinggot"harmonics theeife V of a"151 'ogi-*essive ehange tifeqne-nfcy. In A v .the ease: of 2 continuous Wave-there is e single; frequency and -the -part-sloth Wave {extent 'dedneihl e fitoni chameteristies of the offt1ie pat11toward the'iand side-hes direction, to the wa vedirectly received firo n" the source f om thefibeginning of radio de i 853,1noted above, tof

wave leng nnde' n'ped He found it i I s lue i qi f ih eve. Whether fby trans'mission-;has i'heen universally used so f alfas' known in direction finding systenisii.

end it is belieyed that damped wave trans m e.- 5%? e e y anclif a 510mg? time recognized frfp u'posefl directly received Wave and a Wave of Waves which n reach the receiver" aftei pursuing; 2i

devious path which is not readily; deter lninedi Except? for reflection" and v en-magi; i eftcts'these undeeii-edWa eS would not'be the ino st eii'eetiife} this:

The; edvanta'g'e derii'ed fi'omfthe nee. o f dampedwiwesmayibe accounted foron the tense phenomena are impossibleflfrom -a' lnentjof inteiferenee atthe-"ireceinjeig' si'nee i the: la teiz end ot. oneFtrain'"might arrive.

atthelsametiine as the beginning of an adin pert at least, by the pi esenee of a pi-e1 Ween entielk successive eltern etions due to r d (p e'irticular' wave length I V 1 pediated-s These conditions: mak dfiIi1te a1 1d persistent Interference ph'enomenz (unit of a We've sini-i la gai n 2 1 11 irespeetsezeeptk3 S nal 1 th 1. f

kitat-aiel; as a c lepho'nef from th i and ithenetore'j notgceiising memes in the direction of the transinittin z sta .on

;.i ts-0** longfl va-ve; length; as competed vW 'hjehort V it rney he poinrtedlontn 1 Th eves the peth difieitence ;n1eesnre in fi'va"velengths; betn een different-paths of 1 reflected"(in-refracted? The greater hieans 'lhe present entimrwescol V a "of the sl m 56m t at the ehnees o f'dnu'tiie'h'iliterierenee Q 'effects'are inc'iieasedf n a nsom what s'nnfl proportion;

v aiipirent 7 V 'tion of the calling ship and informing her or two of the high power transoceanic stations, which are so few in number and so differentiated .trom each other by known characteristics as to be readily distinguished and identified. Or, as another example, in

the case of transoccanic airplane flight, it would be highly desirable to maintain continual contact with a shore station or stations throughout the voyage. This, again, would require the use of high power stations. The one common characteristic of these stations is that they are each equipped for undamped wave transmission. Accordingly, the use of spark signals at the reference station is at once ruled out. It woulc be a very simple GXPQCilQRt to send out the undamped waves, characteristic oi the radiation from'these stations, modulated by a signal containing many frequencies, as by a modulating source the frequency of which 15 continuously and cyclically varied by mechemical means. The modulations, separated cut in the output of a detecting tube, would be similar in all characteristics affecting accurate direction finding to the highly damped wave which has heretofore been used. It is accordingly the essence of the invention to simulate the conditions obtain- .ing in the damped wave signal by means 01? modulations of an undamped Wave, the said modulations being caused to have a continuously varying frequency.

F or a description of the invention in aspecific embodiment, reference is made to the following description taken in connection with the appended drawings, vherein is, disclosed, in Fin. 1, circuit diagram of a transmitting station which embodies the idea of the invention. Fig. 2 shows the circuits a receiving station which may be used with the transmitting station illus ated in Fig. 1.

Referring to Fig. 1, th figure, as whole,

is illustrative oi": simple circuit arrangement by means of which it is possibleto tlill'lfillllh modulated carrier frequency signals. The various elements which go to make up the system are each old and require little explanation. The reference ordinal G indicates a conventional. circuit arrangement oi an oscillator, the particular oscillator chosen being of the well known Hartley type. This oscillator is a source of the carrier frequency oscillations, the frequency of which may be-varied by adjustment of the constants of the oscillatory circuit associated therewith in a well known manner. The carrier waves are'modula-ted by the lowfrequency Wave emanating from the low-trequency source G by means of the modulator the addition of other amplifiers in parallel with those shown and by the addition of groups similar to that shown, in series. In this manner, the capacity may be sur'liciently increasedto provide even for transoceanic transmission. 7

For the modulating means a low-frequency generator G, is here shown as replacin the usual microphone means. The frequency of oscillation of this oscillator is continuously and cyclically varied by a me chanical actuating means operatively connected 'to the movable element of the condenser, which consti utes with the coupling inductance, the oscillation circuit of the gen orator. ()ther means for modulating the carrier wave with a signal of many frequenciesmay be employed, that shown being perhaps as simple and obvious a means as any to accomplish this purpose. It is ob vious thatavoice modulated carrier wave would be equally as effective, although possibly not as adaptable for practical purposes. I

Fig. 2 shows the receiving circuit which is related to the transmitting circuit described above. Any dir ctive receiving system whatever is adaptable to the purpose of the invention, that shown being illustrative of a common type. y

The detector 1) and the amplifier A, in the output circuit of which is connected the indicating instrument, require no explanation except the statement that they her function as they doin any receiving circuit ofwhich they may form 'a part. The particular directivemeans shown is one of the several forms embodying the well ltnown Bellini-Tosi principle. In the arrangement illustrated, two antennae are mutually related to the input circuit of the detector. The antenna 1 has no directive characteristics and its presence in the circuit results in a continuous sound in the receiver. The antenna 2 is capable of being rotated about the vertical axis, as shown, and has an electromotive force generated therein by imping ing radio waves, the amplitude of the electromotive force depending on the presentation of the antenna to the direction of the incident waves at the particular moment. In general, the eliect is a maximum when the plane of the antennae isparallel to the direction of the iiioidenflwaizeg, a ncljis" mini-' 'ly rotated until the positiongofmaxi mimlor minlmunistrength of s gnals s ifound' the nultposition of the antenna being usually more effective in makingthejsettiiigs The System would function efiiciently if the 5am V tehii-a: 2 were aloneused, but the presen'ice of ,straysand statio woulditend to broadenthe direetivity jcuirve close to its minimum point" and it has beenifound to be better to'operatei 5 around a minimum which corresponds .foughly .to a i ormzil intensity of received] P signals. To this eiid, the antenna 1 is used; z Thep re'senceof a1 signal inQthe ifGCBiVGYJl-itV- ing'a' constant inteiisity, 'due to this antenna, 7

tendsto drown oiitfthe undesirable" static i Qf diusfin n t eapparatus Aned- ,ditionallfunotioi of the vertical aiite ip a; l

"is to eonfilietlfl'e'fieldbfdireiltive influence to 7 but" it single-direction in; the plane oijthe 'antennaIZ-flhe polarfdiag-i-gtm which i nclica tes by its radius seotortl e selectivity :of/ "Ethe system Comprising antenna 21 3 figure of eight ouiv ewhioh may be rep res ented two tangent ci 1e ,The superpositio 'ciiicle representing the radiation diali iofhe ve ca nten a ithe tri addition thereof fi'nj regard vto direction r'eing; to know his'fp'osition would Iobten e 7' Sll lfis ij-ni a'h'ea tshaped: curve Iwhiohincliat'es therdireotivityjina; single-direction; Refer- 'e ce is ihadeto pages 6 3310 635 of Flemingf Ther Principles of Eleotrioiyaye Telegraphy and Telephony third edition, :forfor. thei-fdis'closu e oftlieroperation, of this :tvpe

of appa ratus. QTh'ere is-sliown, on intliczptiiigf ,mez'pns associateclwiththe-"movable portion;

of the antenna, by i means of whiqhiheldirecs ;tion of incident 'wzives 51113315 be dete inixied. v, If it" is desired to receive I signals from; certain predetermined}frefereiice stations, 1 the 1 iieoeivin gciifouit may-be brogidljr ,tl 'edk to gthe corresponding transmission 'statioii sfso that either fpmny e ofytheI-refei'e ice tat o s m ye p ed up by weepin 4 1 antenna over asufficiently jaiig11ia ri;{;a;;ge.=

Afterpicking upthe desifQcI-stetion,;t1iefoii Quit ma-y be timed to-f.thefpartioulajif qiiency. In practiealsope ation; gcco 1y," an attendant at the recifving stetion d i1"- whatever; j'

hez jipg intupooiieeoh of U YO O IKI HOEQ refs T e encefstatioils af hi l1 e -Q E cl'e elfjmine the position by; mathematioztlg-oalculareference stations? nayfby: predetermined armngementg send, out the Signet modulations' a't ;1; eeitailnivand known time-311d each 7 station may ieasily be distiic gu-islied 'IEI fiOIli the other ffstations by; a iparti ilar, inod ulating" characteristic.

Although i Fig. 1 therelis" shown, it methodof modulating an undan pegl wave; it should be uiiderstood that'this is illustm -i v V t ive only of oiiel possible. means forfmodify V 1 ing the character; of V unda-lnped Waves and and:stmys as well as to inc ease thesen sitiv in I simolationiof spark transmissio n'2 involving i he"us e m n da ped w es by a m ans What is claimedisz V i '1, Themethodof di fectionfindiiigfwhieh .wmp i' ret n fa o i ind uswe," 'n odulati g S 3 ,idWa,VeiIl" zto ooifdan ce' with a wave having 2i, "eyclically QlldjcdffiiHuOuSly f j'v ryin w y: f i h eby} S mulate. 1 damped wave and therefore to: ifisure. itsf rectilinear propagation, ,rectijli e arlyth nsp I mitting said modulated waxies ingall dir v 4 'tions, and; dirf tivel-y-recei ave and therefore to ii sui e IYBCtiliIiQiiiPijQg V 2; The neth0d'o determ ning vthe \id'iIfGC i m a mob lere e v nestati n.wi h r f-' erence to Le fixed transmittinj'ggstetioii; which Q 1 Consist-s generating; afigfll'ldalhpd iv ave at? the rfixedfstatioii," leastfparltia11 y 'mod'ulz tfdog said wave 'in accordance-with swam 1 having z cyclically andjcontinuous ly varying I "frequency to theifeby-sililiilate 'zin -iiiidem' qed P s-M re l ne l a te i tine tin 11 d rect ons said Wave,, e1 d1ng' =thelmochi incidences"- 

